A 17-year-old from Darwin will spend a minimum of 12 days in detention for the bashing of a sleeping homeless Aboriginal man.

The young man, from Wanguri, was sentenced by a Darwin magistrate to eight months imprisonment for the unprovoked attack in February.

Magistrate Daynor Trigg said the attack, involving the youngster and a group of four friends, was cowardly, unprovoked and violent.

The 42-year-old victim's jaw was broken and he required surgery at the Royal Darwin Hospital.

Mr Trigg said it was unclear whether there was a racial motive for the attack and admitted to a degree of difficulty in finding a suitable sentence.

In suspending all but 12 days of the detention period, the magistrate said he took into account the guilty plea, good rehabilitation prospects and the fact that it was a first offence.

Mr Trigg imposed a good behaviour bond for 18 months. The other four are yet to be sentenced.